The research will attempt to assess the relationship between cell surface function and biological senescence. In particular, membrane transport will be studied in human diploid fibroblasts in early and late passage. Earlier observations relating a decline in transport rate to increased passage number will be critically evaluated and extended. Since the free amino acid pools influence transport rate they will be analyzed simultaneous with transport. Cell surface glycoproteins relate both to transport and other cell surface functions; therefore their structural properties will be studied. Particular attention will be given to surface binding molecules.